Automatic control for reversing propellers



March 24, 1953 M. E. LoNGFELLow AUTOMATIC CONTROL FOR REvERsING PROPELLERS Filed Nov. 26, 194e v 2 SHEETS-SHEET l INVENTOR Mezz/n E. Loaz'y/e ZZo w ATTORNEY March 24, 1953 NLE. LoNGFELLow 2,632,516

AUTOMATIC CONTROL F OR REVERSING PROPELLERS INVENTOR MeZwa'wE'. .Lofeow www Q ma' ATTORNEY fthe pitch limitmechanisx'n;`

Patented Mar. 24, 1953 AUTOMATIC CONTROL FOR REVERSING j PROPELLERS Melvin E. Longfellow, Manchester, Conn., as-

-signor to United Aircraft Corporation, East Hartford, Conn., a corporationof Delaware Apiiictii Nvhibgr 26, 194e, serial No. 712,402

1A l l i 'lhis invention relatesto hydro-controllable 'prepellersiof the type which may'fb'e feathered Or reversed andparticularly to imprdvedcontrol mechanism operativeY duringY unreverfsing "of the Propellervbladsf i l 1I Y n In propellers having a high rate of pitch change fsoine automatic, quick-acting means must l be provided to insure the return of the propeller to the governor controlled,n constant speed range Whnthe propeller is unreversed. Otherwise the blades {vill bejpositi'ohed against the high pitch 'constant speedV range" stop before theirrelease 'to constant lspeed operation.

` f'this invention to providefimproved means, `operative during unreversingof fthewpropellerffor automatically returning the propeller to ,the constant-speed, governor-conyAnother object of the invention is the provision 4ofielectrically operated means for automatically k'to4 improve vthe construction and operation `of Vfeathering-` and reversing propellers.` f A `Theseand other objects and advantages ofwthe inventionv will be apparent from the specincation and claims andV from the accompanying drawings hichshow what' is nOW considered to be aV pregferdvembodiment of the invention,m n if lIngthese drawings;` l

, Fia` .1 .is adiagrammai@ ,View 0i the. Ditch. .76.91.1- trol means of a hydraulically"actuated, constant 4speed,4 feathering andy reversing propeller em- 'bodying the invention;

Fig. 2 isi a longitudinal'sectional vievv through Fig. 3 isa sectional view of lines -3--3 offlig..

ure 2. .A

"*Referring tothe dravvings in detail nand particularly to Fig. 1,the numeral l0 generally in- Mdicaltes a Ahydro-controllalcle featheringftype propeller having a hub il, and the numeral I2 generally indicatesthe propeller driving engine from which the propeller', drive shaft, generally indilcated'at|4,Yprojects. The propeller'lll r`is provided with suitable pitch changing apparatus and is shown herein as having an individual vvane type hydraulic motor for each blade,.one of s uch Ymotors being shown diagrammatically in section V@in Fig. 1 and kgenerally indicated at I6. Each `motorhas an outer movable portion lconnected to the corresponding propeller blade and pro- 'iidcd with.VA iwqodiameirically; opposed: Varies, 2.0 Y y i4 Claims. v (o1. 17o-160.2)4

'distributing valveV 34 so that the latrefvaive w11 Questioned to change me, pien. of t j and 22 and an inner fixed member 24 provided withV two diametrically opposed vanes 26 and 28. Fluid isV supplied to the pitch 'changing motors of the several blades from a suitable pressure source, such as the pump generallyindicated at 30, rotatable with engine driven shaft I4 and having'piston plungers 3l reciprocated by a normally relatively xed cam 33. From pump 36 fluid is conducted through the pressure conduits 32 leading to thedistributing Valve generally indicated at 34, and from the distributing valve selectively to the conduits 36 and 33,V depending upon the setting of the valve asgpositioned` by the governor to determine the direction ofi-propeller pitch change. When hydraulic fluid` under pressure is supplied through one of ,thelines 36 or 38 to one side of the pitch changing motors, fluid Will drain from the Opposite `side of the motors through the other line to valve' 341-from Which it will be conducted through the conduit 40 to the sump, or reservoir, 42 connected "With the intake side of pump 30. The` pump `30 and the sump 42 are located inthe propellerhub and the pump plungers 3l are reciprocated during rotation of the propeller byrotation around stationary cam 33. M 1 -f The fluid distributngvalve 34 iszalso located in the propeller hub and rotates therewith; This valve is controlled by a speed responsiveigovernor vgenerally indicated 'at 43 driven from the engine I2 by a suitable gear drive including a;gear"44 on the governor drive shaftf45 and a gear 46 concentric withf and rotatable. With shaft 14; ias shown in the diagrammatic Vshowing of 1. The governor '43 includesY a set ofV centrifugally actuated fly balls 48 which act to -moveas Slide valve 50 in opposition to a Speeder spring- 52.The slide valve 56 reciprocates ina fixed valve lcylinder 54, and the side walls of thevalve ,andvalve cylinder are provided with registeringports in a usual manner Which control ther V110Wy Of:.uid

through the governor. A`fluid pumpv 56, shown herein as of the gear type, is driven from governor drive shaft 45 and supplies pressure iiuid from reservoir throughconduit 62, constant'pressure valve 64 and conduit 66 to the governor which, `when its ports Vare'aligne'dfadmits high pressure fluid to conduit 68,normall`y'open solenoid Operated valveA, conduitsl and-121:0 the servo-motor 'l4.l Servo-'motor 14`ope'rate's" i a piston rod 'I6 connected through thfdisplacement mechanism '18' and rotational slipgomt 60 with the plunger 82 of the pitchY controlling; fluid peller in response to demands by the governor for increase or decrease in the speed of engine I2 and its connected propeller.

Within the slide valve 50 there is a recipr-ocable pilot valve 90 projecting out of the upper end of the slide valve and connected to the end of a lever 92. Lever 92 is pivoted intermediate its length on a xed pivot 94 and is pivotally connected at its other end to the upper end of a compensating plunger 96. At its lower end the pilot valve 90 carries a piston which controls the iluid ow through the governor ports to prevent over-travel of the governor in a'well known manner.

Servo-motor 'I4 comprises a cylinder v98 in which a piston |06 reciprocates anda communicating cylinder |02 of reduced diameter in which an enlarged portion |04 of rod I6 reciprocates. This arrangement provides chambers |06 and |08 onthe opposite sides of piston .|00 having A'.iierential piston areas. Piston rod.'16 extends into-a cylindrical casing |09 and carries therein an abutment l which bears against one end of Atwoconcentric compression springs vand ||2 '(Fig. 3), the opposite ends of which bear against theclosed end of the casing. Springslll and -|-|2..thus opposethe action of the fluid under l'pressure in chamber |66 and constantly urge the piston rod '|6 toward the left as viewed in Fig. l. Flow ofhigh pressure fluid from thegovernor 443 through conduits 68, l0, and 12 to chamber |06 is controlled by normally open lock pitch solenoid valve A. Chamber |06 is connected by va conduit ||4 with the bottom of cylinder ||6 within which the compensating plunger 95 recipfrocates. Withthis arrangement the pilot valve 190 as controlled by the compensator gradually `retards the movement of the servo-motor as the propeller-.pitch approaches an angle correspond- Y'ing to the-speed change demandof the governor. The Agovernor .andcompensator mechanism is -more fully disclosed in a co-pending applicaltion, Serial No. 664,640, filed April 24, 1946, noW yabandoned, and assigned to the assignee of this application and reference is made theretofor a -morefcomplete understanding of thismechanism.

V4Chamber|06 is connected through conduit v12, manifold ||8, a normally closed increase pitch solenoid valve C and conduit |9 with reservoir f -60,.this arrangement permitting fluid.. trapped in lchamber |06 to be vented `aspiston .|0,0-moves to the left in Fig. l under theaction of springs V| and-| I2 to increase the pitchof the blades. Pressurerfluidfromlpump 56 is alsosupplied Athrough conduit |20, normally closed decrease `pitch-solenoid B, manifold ||8, and -conduit 12 'to chamber 4|06 where it acts on piston |00 to `move the blades toward low pitch position.

The valve 34 for distributing fluid to the vane Amotor has an outer cylindrical valvecasing |2| Aprovided with ports |22, |23, |24, |25, and |28. .'Withinrthe casing |2| is a reciprocable sleeveLlS .operatively connected atone of its ends with a 4propeller pitch changing mechanism by a suitable :mechanical connection shown schematically in ,Fig. las a bellcrank |32 and a cam |34onthe Vmovable member I8 of pitch changing motor I6. @The bellcrank is maintained in contact with the cam by a suitable compression spring |36. The V`valve plunger 82 extends into the sleeve |30 and is ,provided therein with spaced valve pistons H|37 and 38 adapted to control ports provided in. the valve Vsleeve |30 which are registerable respectively with ports |22, |23, |24, |26, and |28 in the outer valve casing |2| over the `entire range of relative movements between the sleeve and the casing. Port |23 is connected by conduit 38 with one side of the hydraulic motor |6. Port |26 is connected by conduit 36 with the other side of the hydraulic motor, and the port |24, located at the mid-length position of the distributor valve, is connected by conduits |44 and 32 with the outlet of the pump 30 so that fluid under pressure is supplied at all times when .thepropeller is rotating to this intermediate positioned port.

The operation of the distributing valve 34 is such that, when the plunger 82 is moved in response to the governor demands for a speed changefone side of the hydraulic motor |6 will be connected with the fluid under pressure entering from conduit |44 while the other side of the motor will be connected with the sump 42 through conduit 40, resulting in rotation of the motor |6 to change the propeller pitch. As the pitch is changed the sleeve |30 is movedtoclose oi the connections between the distributingand the propeller pitch changing motor at `afrate such that when the propeller pitch has been changed a number of degrees sufiicient to correct the governor indicated deviation from .the speed ,for which the governer is set, the pitch changing motor will be stopped and it will be-hydraulically locked against any yfurther pitch changing movement until servo-motor 14 again changes the position of plunger 82 inresponse tolgovernor demands. Thus, the positionof the servo-motor 14 and the plunger 82 alwaysindicatesthe,pitch angle of the propeller blades.

The above described mechanism providesy an automatic constant speed control of the `power plant over a predetermined range `of propeller pitch angles, the limits of which is determined by a low pitch limit stop |46 and a high pitch limit stop |48 as shown diagrammatically in Fig.

1 and more in detail in Fig. 2. These stops are adjustably threaded on a hollow adjusting screw |50 which is slidably mounted on a shaft |52 mounted in the housing which supports cylinder |09. The adjusting screw |50 has a `central squared portion over which two forked projections on the bottom of abutment I0 are received so that the screw |50 is reciprocated withl piston rod 1s. A pitch limit solenoid D is provided having a winding |54 and a core 56. Theupper end 0f the core |56 carries a pin |58 which cooperates with two pivoted stop links |60 and `|62 having abutment faces |64 and |66 that cooperate with stops |46 and |43. A light compression spring |68 constantly biases a plunger |60 upwardly into engagement with the core |56 land consequently biases the core and the abutment links |60 and |62 upwardly into stop engaging position. With the abutment links |60 and |62 in normal position shown in Fig. 2, in which the solenoid D is de-energized the reciprocating movements of the piston rod 16 are limited by engagement of the abutment |64 with the low pitch stop |46 on the one hand and engagement of abutment |66 with high pitch-stop l|46 on the other. This comprises the governor control, constant speed, or service, range of propeller blade angle variations.

At opposite extremes of the constant -speed range of the servo-motor '|4 special purpose ranges are provided into which the servo-motor may enter to feather the propeller blades vat one extreme of travel and to reverse the pitch of the blades at the other extreme of travel. Thus when the solenoid D is energized and pulls the is closed. This establishes the following circuits:

.i (8) A circuit from battery 268 through conductor 2|0, switch 252, conductors 256, 251, to solenoid of valve B.

' (9) A circuit from battery 208 through conductors 2|0, 254, switch 252, conductors 256, 258, and coil 260 of relay X.

. (l) This results in establishing a circuit from the battery 20,8 through conductors 2|0, 262, 264 and lower switch 266 of relay X (now in the dotted position), conductor 268 and coil 210 of relay Y.

(11) A circuit is also established from battery 208 through conductors 2|0, 262, 212, switch 214 of relay Y (now in dotted position), conductors 216, 234, switch 236 of relay X (now in dotted position), conductor 213 and coil of solenoid D.

- (12) lThe closing of relay Y also establishes a circuit frombattery 208 through conductors 2 l0, 262, 212, switch 280 of relay Y (now in dotted position), conductors 282, 244 and solenoid of valve A.

(13) Closing of relay Y and depression of plunger |56 of solenoid D, also establishes a circuit from battery 208 through conductor 2li), contacts |14, conductor 284, switch 266 of relay Y (now in dotted position), and coil 210 of relay Y which constitutes a holding circuit for relay Y independent of the above circuit (l0).

High pressure fluid is now supplied from pump 56 through conduit |20, open solenoid valve B, manifold ||8, and conduit 12 to chamber |66, thus moving the servo-motor in a pitch decreasing direction. Since solenoid D is also energized, the servo-motor can move the piston rod 16 in a low pitch direction into the special purpose or reverse pitch range until the end of adjusting screw |50 engages the reverse stop |12.

To unreverse the propeller blades it is only necessary to open switch 252 which de-energizes the circuit through coil 260 or relay X. Relay Y however remains energized through circuit (l0) above. Contacts |14, which are in series in circuit will remain closed, although the relay D is now de-energized because the stop links |66 and |62 are held down by the low pitch limit stop |46 the periphery of which overlies the free ends 268 of these links in the reverse pitch position-of the servo-motor. Y Opening of relay X establishes y (14) A circuit from battery `203 through conductors 2 l0, 262, 212, switch 214 of relay Y (which is in dotted position), conductors 216, 234 and switch 236 of relay X (now in full line position), to solenoid valve C. This permits the nuid in chamber |06 to be vented to the sump 60 as previously described and allows the servo-motor under the action of springs and ||2 to move in a pitch increasing direction. As the low pitch limit stop |46 moves off the links |60 and |62, the solenoid core |56 is moved upward by pin |69 under the action of spring |66 and contacts |14 are opened. This results in opening circuit (13) previously described through the coil 210 of relay Y which de-energizes solenoid valves A and C' and allows the mechanism to return to its normal position with the abutments |64 and |66 in the constant speed range between stops |46 and |48.

Switch 283'is an independent control for the solenoid valve A and is used to lock the propeller in any pitch that it may happen to be in at the time the switch 283 is closed.

It will be evident that as a result of these improvements automatically operable means have been provided for returning a propeller having a high rate of pitch change to governor controlled, constant speed range when the propeller is unreversed.

Further, means have been provided by this invention for automatically returning a propeller of this type to governor control at a predetermined pitch setting during unreversing.

While only one embodiment of the invention has been shown and described, it will be understood that various changes in the construction and arrangement of the parts may be made without departing from the scope of the invention as dened by the appended claims.

What is claimed as new is:

1. In combination with a propeller having controllable pitch blades, hydraulic means for controlling the pitch of the blades including a servomotor, cooperating fixed and movable stop means normally limiting the movements of said servomotor and defining the service range of the propeller, means operatively connecting said movable stop means with pitch controlling means for movement therewith, a constant speed governor controlling said servo-motor throughout said range, a plurality of electrically actuated means connected with and controlling the operation of said servo-motor and one of said stop means for disabling said stops and moving the propeller blades beyond said service range into reverse pitch, means for energizing a selected group of said electrically actuated means including said stop disabling means for reversing the propeller, means for energizing another selected group of said electrically actuated means for unreversing the propeller, switch means connected with said another selected group of electrically actuated means and with said one stop means and actuated by the return of said one stop means into position to cooperate with said other stop means for automatically deenergizing said another selected group of electrically actuated means and returning the propeller to governor operation and manually operable switch means controlling the operation of both of said energizing means.

2. In combination with a propeller having controllable pitch blades, hydraulic means for controlling the pitch of the blades including a servomotor, a governor and a plurality of electrically actuated valves controlling the operation of said servo-motor including a lock pitch and governor disabling valve, a decrease pitch valve and an increase pitch valve, cooperating stop means preventing pitch changing movement of said servomotor beyond predetermined limits to dene an intermediate service range of blade pitch variation, means operatively connecting at least a portion of said stop means with said pitch controlling means for movement therewith, electrical means for retracting one of said stop means out of cooperating position for conditioning said servo-motor to move said blades into reverse pitch, means including a relay for energizing said electrically actuated lock pitch and governor disabling valve, said decrease pitch valve and said stop retracting means for disabling said governor control and said stop means and moving said servo-motor into reverse pitch, a second relay having a holding coil circuit energized by the closing of said rst relay, said second relay controlling the energization of said lock pitch and governor disabling solenoid and said increase pitch solenoid, means including a pair of contacts in the holding-coil circuit of said'pitch changing mechanism, manually controlled means operatively connected with said control for setting said control for changing the pitch from said special purpose range to said service range, a mechanical pitch limit stop having cooperating relatively movable parts relatively movable with pitch changing movements of said propeller and dividing said ranges, manually controlled means for disabling said stop, means forautomatically rie-activating said stop incident to changing propeller pitch from the special purpose range to the service range, and means operatively connected with said stop and said manually controlled means maintaining said control in operative position while the pitch is changing from said special purpose range to said service range and means forming a part of said control automatically actuated responsive to reactivating action `of said stop to automatically disable said control. Y

` 4. In a controllable pitch propeller having a service range of pitch change and a special purpose range of pitch change beyond said service range, pitch changing mechanism, agovernor for controlling the propeller pitch within said service range, other means for controlling the propeller pitch outside of said service range including means for disabling control by said governor, means for automatically restoring control by said governor upon return of the propeller pitch from outside said service range to within said service range including a two part device having relatively movable parts and means operatively connected with said mechanism fory relatively positioning said parts in accordance with propeller pitch, control means operatively connected with said device and actuated thereby responsive to movement of said parts past a preselected relative position, means operatively connectedwith said other means for disabling said other means, means operatively connecting said control means with both said disabling means to automatically disable said other means and restore-control to said governor upon actuation of said control means.

`5. In a controllable pitch propeller having a service range of pitch change and a special purpose range of pitch change beyond said service range,pitch changing mechanism, a governor for said mechanism, a first electrical means connected with said mechanism for controlling the propeller pitch outside of said service range and a second electricalmeans for disabling control by said governor, means for automatically restoring control by said governor upon return of the propeller pitch from outside said service range to within said service rangeincluding a two part device having relatively movable parts and means'operatively connected with said blades for relatively positioning `said parts` in accordance with propeller pitch, a rst switch means for disabling said lrstelectrical means, a second switch means for disabling said second electrical means and Vto 10 means' operatively connected with both said switch means and with said two part device and actuated thereby responsive to movement of said parts past a preselected relative position to effect actuation of both switch means to restore control to said governor.

6. In a controllable pitch propeller having a service range'of pitch change and a special purpose range of pitch changeV beyond said service range, pitch changing mechanism, 'a governor for'said mechanism for controlling the propeller pitch within said service range, a first manually controlled means connected with said mechanism for controlling the propeller pitch outside of said; service range including means for disabling controll by said governor, said pitch changing `mechanism including a two part 4device having rela-1` tively movable parts -an-d means for relatively positioning said parts in accordance with propeller pitch, control means operatively connected with said device and actuated thereby responsive" to movement of said parts past a preselected relaf tive position, means operatively connected` With"- said nrst manually controlled means for dis-` abling the same, means operatively connecting. said control means with both of said disabling"` means to simultaneously automatically disable said first manually controlled means and restore control to said governor upon actuation of said control means.

7. In a controllable pitch propeller having a service range of pitch change and a special purpose range of pitch change beyond said service f range, pitch changing mechanism including a two part device having relatively movable partsand means for adJusting the propeller pitch in ,Y accordance with the relative position of said parts, a governor operatively connected with said mechanism for controlling the propeller pitchl within said service range, a first manually controlled means for moving the propeller into reverse pitch position, a second manually con- 'e trolled means for disabling control by said governor, and a third manually controlled means for moving the propeller from reverse pitch into said service range, control means operatively connected with said device and actuated thereby" responsive to movement of said parts past a preselected relative position in passing from reverse pitch position into said service range, means operatively connected with said third manually controlled means `to disable the same, means operatively connecting said control means with. both of said disabling means to simultaneously automatically disable said third manually controlled means and restore control to said governor upon actuation of said control means.

8. In a controllable pitch propeller having a service range of pitch change and a special pur-` pose range of pitch change beyond said service. range, pitch changing mechanism, a governor y connected with said pitch changing meansfor controlling the vpropeller pitch within said service range, electrically actuated means connected with said pitch changing mechanism and said governor for controlling the propeller pitch outpeller pitch from outside said service range `to within said service range including a two-Apart'` device having relatively movable parts and means i connecting one ofsaid partszwith saidpitchv4 changing mechanism` fo'rv relatively positioning.

side esaidlservicerange .to-disable said*v electrical.

controlmeansrand restore' control .5 to said governont` 9.-.In'jalcontrollab1e pitch propeller having pitch changing mechanism and controls therefore, pitch .Y

limitrcstop meansxshaving Vcooperating relatively movablerparts :one ofcwhiclr-partszis: operatively connected: withv and mo.vablef.with said pitch.

changing mechanismaiorlimiting @movement of..

saidrpitchclfiangingfmechanism,means.operativelyJ connecting said stopV means` andsaid controls forv disabling said stop means-,means operatively connectedwithsaidstopmeansand saidpitch chang=. ingr. mechanism-for A.automatically re-activating said stop means responsive to pitch. changing.

movement or fsaidpitchchanging ,mechanism,. a device :connected lvvithl said stop means and with saidcontrolsland.movable`,by disabling movement ofjsaidlstodmeans, intoposition to maintain a portion -of said, controls energized,V means. operativelyllconnecting.-said-.device with said .stop reactivating meansjor movement thereby, said de;

vice4 .being movable by said re-activating means inits re-activating movement to de-energize said portion of said controls.

10.A In. combination..with a propeller having controllable pitch. blades,` hydraulic 'means for controlling the pitch' of .the .blades including. a servoemotor, stop mechanism comprising high and "loWpitch limit' "stops .connected with, and movable 'with,'"said pitch. controlling means and a retractable stop normally biased into position between saidliinit stops and,vvith said limit stops; defining lthe constant' speed range of the propeller blades; 'a constant speed governor controlling said servoimotorin saidV range, means automatically returning' 'said' retractable stop` to said position uponrreturn of said propeller Ablades 'to said range from* beyond said" range," said propeller blades f having'faY specialfrange'beyond said constant 'speedf range"vr in: .whichf the blades' are 'in .reverse `pitch; a -rstr electrically actuated-means connected with'.

said governor fand" operativewhen 'energized toV disable"1sa1`dl governor, f a `'second electrically actu'- atedmeansfconnected with .said servo-motorV and H operative lfvvhenl energizedftdcontrol movement of said .blades by saidhydraulic means in returning said= propellerbladesfrom saidA special range to saidggovernor controlled range. and electrical means. operatively connected-With-said cooperating stopmechanism and .operatedby the latter when said retractablen stop returns to its normal. positionbeyondsaid limit stops, means opera-- tivelyconn'ecting said electrical means and said electrically actuated means, said electrical means, when" operated,"de-energizing"both said electrica1ly"factuated "means to return said propeller .to governor'controlf 115 In` combination' with a propeller having.

controllable pitch blades, hydraulic vmeans nfor controlling` the `pitch-'of the blades including a servo-motor; low pitch 'limitstop vmeans having a portion operatively connected with said pitch controlling means `and preventing .movement `of said servo-motor beyond a predetermined limit'V and dividing a' constant speed range'. for the propeller bladesfrom `a reverse pitch range, a speed governor controlling said. servo-motor in said constant speed range', electrically actu-f ated'means for disabling control by said speed governor,VV means f for `disabling said-limit .stop means;H means l for automatically re-activat-Y ing saidilimit stop meansuponr return of said. propeller blades `to vsaid constant speed rangefrom said reverse. pitchV range, electrically actu-r ated :means .controlling the.. movement .of said blades'by sai-d hydraulicsmeans .in said returnV andswitch .means actuatedby said low pitch limit. stoprmeans, means operatively connecting saidl switch meansV and both .-saidf electrically actuated means and means vconnected with said connecting.

means and eifectiveupon actuation of said switchA means .by re.'-activation oi said limitstop means. to disable both of said electrically. actuated means. to returnsaid. propeller automatically. to governor control when the propeller enters-constant speed range from the reverse pitch range.-

l2. In a propellersystem, a propeller having. controllable pitch blades,` and havinga constant speed lrange and a: reversey pitchrange of pitch.

adjustmenty vhydraulic -rneansior Vcontrolling the` pitch. Yofthe-.blades Vincludingfaspitch changing, servo-motor operatively connected with.. saidv blades, low pitch limit'Pstopf'meansfoperatively connected with said pitch-controllingfmeans and-- -lpreventing movement .ofsaid servo-motor beyond.

draulic means insaid reverse range,.means.opera tive1.y connected .with said hydraulic..means restoring saidstopmeansupon return of saidr blades fromreverse pitch rangeto constant speed range,. and a vswitch actuatedby. saidstopmeans andr orminga part of the ..electricalcircuit for saidv electrically' actuated ..1neans .for disabling said electrically. actuated..means..andreturning said.

propellerto governor .control upon return. of-.said. blades to the constant speedrangm.

" 13..Iii a propellerlsystema propel1er..having.,

controllable pitch blades, hydraulic pitch .controla lingY means for. controlling. .the `pitch of. .the blades including a pitch changing hydraulic .motora a` distributing valve hydraulically `connected..with...

said. motor for controlling said motor and a servomotor connected withandcontrolling. said. valve.. low .pitch limit stops connectedwith,Y and movable Y with, said pitch controlling means, and Va retractiblestop engageable with said limit .stop .for limiting the pitch reducing movement of said. servo motor, means .connected with said retractible-stopv for retracting said .retractible `stop to permit movement into reverse pitch, means holding said retractible stop retracted While the blades arein reverse pitch, a sourceof iiuid under. pressure,.a.

speed governor connected with said source and-, said'servo-motor' and controllingthe flow -of said fluid Ato rand from said servo-motor, a lock'pitch solenoid valve connecting said governor and-said..

servo-motor and 'When'en'ergzed blocking flow between said governor and said servo-motor, an increase pitch solenoid valve connected with said servo-motor and when energized controlling fluid for moving said servo-motor toward high pitch, relay switch means connected with and controlling said solenoids, including a relay -having a holding coil, contact means in the circuit for said holding coil and means operatively connected with said retractible stop releasably holding said contacts in closed position when said retractible stop is retracted and said propeller blades are in reverse pitch.

14. In a controllable pitch propeller having pitch changing mechanism and controls therefor, a mechanical pitch limit stop means operatively connected with said pitch changing mechanism for limiting the movement of said pitch changing mechanism, manually controlled means connected with said stop means for disabling said stop means, means connected with said pitch changing mechanism for automatically re-activating said stop means, control means operatively connected with said stop means and actuatable by disabling and re-activating movement of said stop means, means connecting said control means and said controls to operate at least a portion oi said controls, said controls including` further means connected with said control means and actuated responsive to re-activating action oi said stop to automatically de-energize at least a portion of said controls.

MELVIN E. LONGFELLOW.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,346,007 Chillson Apr. 4, 1944 2,378,938 McCoy June 26, 1945 2,402,065 Martin June 11, 1946 FOREIGN PATENTS Number Country Date 560,522 Great Britain Apr. 6, 1944 

